Apparatus and method for counter-balancing a weight balanced reciprocating machine



y 1965 E. w. PATTERSON 3,192,797

APPARATUS AND METHOD FOR COUNTERBALANCING A WEIGHT BALANCED RECIPROGATING MACHINE Filed April 13, 1959 3 Sheets-Sheet 1 2 l u a. a {I E 9 h Q1 W .5 a a, w w m r 2 P 4\ 1 e 8 n .W. y w; 5 e k W w w a w m .w :33: w 05 2 a3 .9 Xx 6 w 0 a ..w z 4. &w

y 6, 1965 E. w. PATTERSON 3,192,797

APPARATUS AND METHOD FOR COUNTERBALANCING A WEIGHT BALANCED RECIPROQATING MACHINE 3 Sheets-Sheet 2 Filed April 15, 1959 y 1965 E. w. PATTERSON 3,192,797

APPARATUS AND METHOD FOR COUNTERBALANCING A WEIGHT BALANCED RECIPHOCATING MACHINE Filed April 13, 1959 3 Sheets-Sheet 3 Mar GD 2 r 4 r551 "551 .v.. 340 E: e52 542 355 .--3544 z @549 14212473250; INVENTOR.

Uited States Patent AZ EARATUS AND METHGD FGR CGUNTER- BALANQENG A v EIGHT BALANCED REG?- RGQATENG MAGIHNE W. latterson, lid-iii fild River School Road,

Hewney, tlalif. Filed Apr. 13, 195% Ser. No. $596,131 11 Claims. (Cl. 74-591 The present invention relates generally to weight-bah anced equipment, and more particularly to equipment embodying one or more counterweights which can be adjusted either manually or automatically to bring the equipment into balance whether it is stationary or in motion. The present application is a continuation-in-part of my copending application Serial No. 649,095, filed March 28, 1957, now abandoned, entitled Apparatus for Automaticaliy Counterbalancing Weight Balanced Pumping Machines.

The present invention is particularly adapted for use in adjusting one or more balancing weights of a weight-balanced pumping machine of the type employed in oil fields, to adjust or place the weight or weights associated with a pumping unit in balance.

The usual oil field pumping unit operates to reciprocate a string of steel rods which are joined end-to-end. Each rod is approximately thirty feet in length, and the joined rods extend downwardly into the well to a pump which is normally located near the bottom thereof. It is not uncommon for such a string of rods to weigh as much as 10,000 pounds or more.

In order to minimize the stresses in a pumping unit that serves to vertically reciprocate a string of rods as described, it is necessary that the Weight of the rod string be canceled out by means of counterweights. In addition, the weight of one-half of the actual fluid load being lifted in the bore hole by the string on the upstroke thereof must be canceled out. This cancellation of rod weight, and as nearly as possible, one-half of the actual fluid load, is accomplished by the use of counterbalance weights that are fixedly positioned on the crank arm or the walking beam of the pumping unit. However, it will be apparent that as the height of the fluid column in the bore hole changes due to any one of a number of physical conditions encountered in the production of oil or fluid from a well, the counterbalance weights no longer balance the actual fluid column present, but are either underbalanced or overbalanced relative thereto. An overbalanced or underbalanced condition in a pumping unit is highly undesirable, for the unit is subjected to undue stresses and strains created thereby.

In conventional weight-balanced pumping units available heretofore, the only possible way to reestablish the balance of the unit when variation in height of the fluid column in the bore occurs, has been to stop the unit and manually adjust the position of one or more of the weights. However, to move one or more of these counterbalance weights when the pumping unit is shut down, requires a crew of men which is not only time-consuming, but expensive.

The primary object in devising the preferred form of the present invention is to provide an apparatus for use in automatically adjusting the counterbalance weights of a pumping unit during operation thereof to place it in a balanced condition as the height of the fluid column in a bore hole varies and with assurance that the unit is at all times in balance. First and second alternate forms of the invention have also been provided by means of which a single operator may adjust the counterbalance weights of a pumping unit during operation thereof to place same in a balanced condition.

A further object of the present invention is to provide invention.

an apparatus for automatically adjusting the position of a counterbalance weight on the crank arm or walking beam of a pumping unit of the character described, which apparatus is completely self-contained on the crank arm or walking beam, and automatically operates to balance the unit upon any change in the height of the fluid column in the bore hole with which the invention is associated during operation thereof whereby it is unnecessary to shut down the unit during such adjustment as required heretofore.

These and other objects and advantages of the preferred and certain alternate forms of the invention will become apparent from the following description thereof when taken in conjunction with the accompanying drawings illustrating same in which:

FIGURE 1 is a side elevational view of a conventional oil well pumping unit showing the preferred form of the invention mounted on the crank arm thereof;

FIGURE 2 is a side elevational view of the preferred form of the invention shown partly in section and associated with a weight-balanced crank arm;

FIGURE 3 is an end elevational view of the adjustably movable counterbalance weight shown in FIGURE 2 taken on line 33 thereof;

FIGURE 4 is an enlarged longitudinal cross-sectional view of the preferred form of counterbalance weight-adjusting device that is utilized in the fully automatic version thereof shown in FIGURE 2;

7 FIGURE 5 is an elevational view of the preferred form of the invention shown in FIGURE 4 just before it reaches the lowermost position in the cycle of rotation;

FIGURE 6 is a schematic view of the 360 cycle of the crank arm;

FIGURE 7 is a combined side elevational and vertical cross-sectional view of a first alternate form of the invention; and

FIGURE 8 is a combined side elevational and vertical cross-sectional view of a second alternate form of the With further reference to the drawings for the general arrangement of the preferred form of the invention, a conventional oil well pumping unit 10 is shown that includes a horizontal base 12 from which the usual Samson posts 14 project upwardly to pivotally support a walking beam 16. Walking beam 16 includes a conventional horsehead 18 from which reins 20 extend downwardly to removably support the upper extremity of a pumping rod R to which the string of steel rods described above but not shown, is affixed. A pair of vertically swinging pitman rods 22 are pivotally connected by the first ends thereof to the walking beam 16, and the second ends of these rods are attached to crank pins 24. Pins 24 project outwardly from crank arms 26 that are rotatably driven by a main crankshaft 28 of a prime mover 30.

The structural details of one of the crank arms 26 are shown in FIGURE 2. Shaft 28 of prime mover 30 is adapted to operatively engage a split sleeve 32 at the left-hand end of crank arm 26, and this sleeve is provided with a slot 34 which receives a key 34:; whereby rotary power may be transmitted from the main crankshaft 28 to the crank arm 25. A bolt 36 extends laterally through the free ends of the split sleeve 32 to the left of the opening defined thereby, and the bolt head and nut 38 are disposed on opposite sides of sleeve 32 in such a manner that when bolt 36 is tightened, the sleeve 32 will grip the shaft 28. A suitable lock nut 40 engages bolt 36 and is positioned adjacent nut 38.

The presently preferred crank arm 26 comprises a pair of spaced, parallel side members 44 and 46, which are joined by a connecting web 47. A fixed counter-balance weight is attached to side member 44 by means of bolts 50. This fixed weight may, however, be replaced by one of the automatically adjustable counterbalance weights to be described hereinafter, if extremely wide variations in pumping conditions are contemplated. An end plate 52 is disposed on crank arm 26 (FIGURE 2), and preferably comprises a channel member of U-shaped transverse cross section. This end plate is afiixed to the outer end of the crank arm 26 by means of bolts 54.

A laterally disposed support plate 56 is situated on the inner end of crank arm 26. Plate 56 is preferably similar in construction to end plate 52, and is mounted on arm 26 by means of a pair of spaced, parallel mounting brackets 58 which are bored to permit fixed positioning thereof on crank arm 26 by bolts 36. Mounting brackets 58 are normally welded to support plate 56.

A piston rod 60, which is normally accurately machined, is mounted below, and parallel to the lower side member 46 of crank arm 26,. and is also parallel to the longitudinal axis of the crank arm. The outer end of piston rod 60 is attached to end plate 52 by a nut 62 which is threadedly mounted on the reduced diameter of the outer end of piston rod 60 which passes through a suitable opening in end plate 52. Similarly, the inner end of piston rod 60 is attached to support plate 56 by a nut 64 which threadedly engages the reduced diameter inner end portion of rod 60 that passes through a suitable aperture in plate 56. A piston 66 is integrally formed on piston rod 60 a substantial distance inwardly from the outer end thereof, and suitable sealing rings 68 are mounted on piston 66.

A movable counterbalance weight 69 is provided that has a cylindrical shell 70 extending therethrough from the inner to the outer edge thereof. This movable weight 69 is mounted over piston rod 60 so that piston 66 fits within shell 70 and the sealing rings 68 are in fluid-sealing engagement with the interior surface of the shell. Weight 69 is slidable between an outermost position wherein piston 66 is near the inner end of shell 70, and an innermost position wherein piston 66 is near the outer end of the shell.

Cylindrical shell 70 has an inner cylindrical head 72 which is brought into sealing engagement with the inner end of this shell by means of a sealing ring 74. Head 72 is bored to receive piston rod 60, and a seal is effected between the rod and head by suitable sealing rings 76.

The outermost ring 76 is held in position by a removable cover 78 that prevents dirt from entering the system. A fluid port 80 is formed in head 72, and has an extension which continues through the head to the annulusshaped space 81 formed between head 72, piston 66, the inner surface of shell 70, and a portion of the exterior surface of rod 60.

An outer cylindrical head 82 is mounted over the outer end of shell 70, and this head 82 is maintained in sealed engagement with the outer end of shell 70 by means of a suitable sealing ring 84. Head 82 is bored to slidably receive piston rod 60, and suitable sealing rings 86 provide sealing engagement between the head and piston rod. A removable cover 88 holds the outermost sealing ring 86 in position and prevents dirt from entering the system. A fluid port 89 is formed in head 82 and has an extension continuing through the head to the annulus-shaped space 90 defined by one face of piston 66, the inner extremity of head 62, a portion of the interior surface of shell 70, and a portion of the exterior surface of rod 60.

A longitudinally extending groove 91 is formed along the upper edge of counterbalance weight 69, as may best be seen in FIGURE 3. The side member 46 is sl'idably engaged in groove 91 to form a tongue-and-groove stabilizer which eliminates any tendency of the movable weight 69 to twist out of position as it rotates with crank arm 26.

In the preferred embodiment of the present invention, the remaining structure thereof is situated in a recess 92 formed in one side of the movable counterbalance weight 69, in the manner best shown in FIGURES 2 and 3.

4 This recess 92 is so positioned as to extend approximately equidistant inwardly and outwardly from the center of gravity of the movable counterbalance Weight 69. A removable cover plate 94 is preferably provided that extends over recess 92.

The structural details of the presently preferred form of counterbalance weight position control device, generally designated by the letter M herein, are shown in FIGURES 2, 4 and 5. The mechanism M, to be described hereinafter, so cooperates with the crank arm 26 that if the torque of the weighted crank arm 26 on its down swing is insufficient to balance the weight of the rod string, plus one-half the fluid load as the rod string moves upwardly, the movable counterbalance weight 69 will automatically slide outwardly a fraction of an inch during each revolution along crank arm 26 until the radius arm through which the weight 69 acts is sufllcient to bring the pumping unit 10 back into perfect balance.

Conversely, when the pumping unit 10 becomes overbalanced because of some change in the pumping load, the preferred form of adjusting device M operates to adjust the movable counterbalance weight 69 inwardly a fraction of an inch during each revolution along the crank arm 26 until the radius arm through which the movable weight 69 acts is sufficiently small to again bring the pumping unit back to a perfectly balanced condition. Mechanism M operates to accomplish this automatic balancing of pumping unit 10 as the load to which the crank arm 26 is subjected varies, without the necessity of stopping the unit 10, and without applying any external forces to arm 26, other than the natural force of gravity.

When the pumping unit 10 is in a perfectly balanced condition, the. time interval required for any 180 half cycle or half revolution of crank arm 26 will be exactly the same as that of the opposite 180 half cycle or half revolution, regardless of the starting position in the cycle of operation from which the computation is calculated. However, when the unit 10 is overbalanced, the crank arm 26 will accelerate when it is moving downwardly from its uppermost position during the 180 half cycle to its lowermost position, and decelerate as it moves back up during the other half cycle from the bottom of its stroke to the top thereof.

A diagrammatic view of the full 360 cycle of the crank arm 26 is illustrated in FIGURE 6. Assuming that the crank arm 26 moves in a clockwise direction, it will commence to accelerate from its uppermost point, all the way down to its lowermost point A. Deceleration commences at point A and continues clockwise until the crank arm again reaches the uppermost point A. However, due to the inertia of the system, no appreciable crank arm acceleration takes place until a point B in the 360 cycle is reached. Likewise, due to the inertia of the system, appreciable deceleration of crank arm 26 takes place only after the arm reaches the .point B in the 360 cycle.

On the asumption that a 20 lag occurs between acceleration and deceleration and the pumping unit is overbalanced, the crank arm 26 will have the same velocity 20 clockwise of A as it has 20 clockwise of A. These positions are designated as B and B respectively, in FIG- URE 6, and it will be seen that in traversing the 180 from B to B, the velocity of crank arm 26 will always be greater than during the 180 when returning from B to B. This means that when the crank arm is moving through the lower 180 from the horizontal position C down past A and B to its other horizontal position C, arm 26 will pass through a zone of high velocity from C to B, and a 70 Zone of low velocity from B to C. Consequently, during the upper half cycle of the crank arm 26 from C in a clockwise direction past A and B and back to C, the arm 26 will move through a 110 low-velocity zone and a 70 high-velocity zone.

It will therefore be obvious that in this overbalanced condition of crank arm 26, it will pass through the bottom 180 half cycle from C to C more rapidly than it will pass through the top 189 half cycle from C to C I whereby the time duration in which crank arm 26 is in the bottom half cycle will be shorter than that during which the crank arm will be in the top half cycle. This differential in time duration of crank arm 26 in the upper half cycle over that in the lower half cycle is utilized in the operation of the counterbalance weight adjusting device M to so automatically position weight 69 as to place the pumping unit It in a perfectly balanced condition.

The annulus-shaped spaces 81 and 953 in shell '70 (FIG- URE 2) are filled with oil or a suitable hydraulic fluid. During the upper half cycle of crank arm 26 rotation, the weight 69 moves down slightly on piston rod 69 and the piston 66 in cylinder 76 forces liquid from annulus-shaped space 9% through port 89. Conversely, when crank arm 26 is rotating through the lower half cycle from C to C, the movable weight 69 slides outwardly on piston rod tl slightly, with the piston 63 in cylinder 7% forcing liquid from annulus-shaped space 81 through port 8%. Dis charge of liquid from space 81 through port 85?, and other flow resistance means to be later described, serve to damp en the outward motion of weight 69 on piston rod 60 during rotation of crank arm 26 through the lower 180 of rotation.

Since crank arm 25 will spend more time in the upper half cycle than in the lower half cycle when overbalanced, the movable weight 69 will move inwardly a small increment more than it moves outwardly during each lower half cycle relative to the arm during each cycle of operation until crank arm 26 achieves a uniform velocity during the entire cycle of operation thereof. Of course, when such uniform velocity is achieved, the crank arm 26 will spend equal periods of time in both the upper and lower half cycles, and inward compensating movement of weight 6? relative to arm 26 will cease when the pumping unit 19 is in perfect balance.

It will be obvious that when the unit is underbalanced, the exact opposite to the action above described occurs, with the crank arm 26 spending more time in the bottom half cycle from C to C than it spends in the top half cycle from C to C. When the crank arm 26 is underbalanced, weight 69 will gradually com ensate outwardly along the piston rod 6% until a perfect balance is again achieved. However, the centrifugal force would interfere with this automatic counterbalancing by movable weight 69 if compensation is not made therefor. Such interferonce is brought about by the fact that during the bottom 180 half cycle of arm 26 the force of gravity is added to the centrifugal force of weight 69, but during the upper 180 half cycle of the crank arm, this same centrifugal force opposes the force of gravity. By means of a freely floating piston 98, best seen in FlGUEiE-S 4 and 5, the weight adjusting device M compensates for this centrifugal force. During the upper half cycle of crank arm as (from C to C) the free floating piston 98 is inoperative; that is, this piston does not interfere with the flow of liquid from cylinder 7% whereby the weight 69 can move inwardly along the piston rod 6% However, when weight 69 tends to slide outwardly along piston rod 6i), during the lower half cycle of arm 26 (C to C) the centrifugal force exerted on piston 93 is utilized to oppose flow of liquid from cylinder 78 to permit weight 69 to slide outwardly on piston rod 6t relative to crank arm 26.

The counterbalance weight adjusting device M (PEG- URE 4) comprises a secondary cylinder liltl wherein the piston weight 8 is freely and slidably supported, and an elongate cylindrical liquid container or vessel H92 that is in parallel disposition relative to cylinder 1%. The secondary cylinder 19%) includes a first cylindrical shell ill =2 in which a second cylindrical shell lfid of smaller diameter is concentrically disposed, with the first and second shells being separated by an annulus-shaped space 1%. Shell 186 is held in fixed spaced relationship relative to shell 164 by a first end piece and a second end piece ill. End piece 110 also includes a cylindrical body portion 112-, the outer end of which terminates in a circumferentially extending shoulder 11 One end edge of shell 1% abuts against shoulder 114, as can best be seen in FIGURE 4. A circumferential groove 116 is formed in body portion 112 adjacent shoulder 114 which is adapted to receive a first resilient sealing member 113 such as an O-ring, or the like. Member 113 sealingly engages the interior end surface of first shell 1&4 positioned adjacent shoulder 114. A central longitudinally extending recess 12% is formed in body portion 112 that slidably engages one end exterior portion of second shell A second circumferential groove 122 is formed in body portion 112 that extends outwardly from the interior surface defining recess 12%, and a second resilient member 124, such as an G-ring seats in groove 122 whereby memher 124 removably and sealingly engages an exterior surface portion of second shell see. A resilient ring 126 is disposed within the interior end confines of shell lilo, abuts against body portion 112, and serves as a cushion to absorb the shock when piston 9% moves to the end portion of shell res in which ring 2 5 is situated.

A first air passage 123 is formed in body portion 112 which is substantially parallel to first shell 1%. This first air passage develops into a second air passage 13% normally disposed relative to first shell 1'84 and extending toward the center or" body portion 122 which thereafter develops into a longitudinal, outwardly extending tapped bore 132. A vented passage 134 extends through body portion 112 from the ambient atmosphere to the interior of second shell 1%, as shown in FIGURE 4. Bore 132. is engaged by one threaded end of a tubular nipple 135, the purpose of which will later be described.

The external diameter or" the second end portion 111 is such that the external diameter of the cylindrical body 149 is slidably insertable within the end portion of first shell 104 opposite that in which body portion 112 is positioned. A circumferential shoulder 142 is provided on the outer extremity of body portion 140, against which,

an end extremity of the first shell 194 abuts. Body portion 149 has a circumferentially extending groove 144 formed therein in which a third ring-shaped sealing me nber seats. Member 146 sealingly engages one end interior surface of the first shell 1%. A fourth groove 148 is formed in body portion 144 that extends outwardly from the interior surface of a longitudinally extending recess lStl, also formed in portion 14% The transverse cross section and diameter of recess 15% is such as to permit slidable insertion of the exterior end portion of the second shell 1% within the confines thereof.

A fourth resilient ring 152 is disposed within the confines of groove 14% and sealingly engages a circumferentially extending exterior surface area of second shell 1%.

Second end piece 111 not only includes the body portion 14% above described, but a second portion ltla as well that abuts thereagainst and is rigidly affixed thereto. A first spring-loaded valve E54 is provided that is intermediately positioned in an air passage 156 which extends through body portions 14d and ldtla from the ambient atmosphere to the interior of second shell 196. Valve 154 is of conventional construction and includes a cupshaped valve member 153 and a slightly compressed, very light helical spring 169. First valve 154 and passage 1545 cooperatively allow air from the ambient atmosphere to enter second shell 106 only when the air pressure within this shell drops appreciably below that of the ambient atmosphere.

A second spring-loaded valve 162 is intermediately disposed in a circuitous air passage 164 that extends from an aperture 165 in communication with the interior of shell 1&6 to an aperture 163 communicating with space 1%. Second valve 162 includes a cup-shaped valve member and a slightly compressed, very light helical spring 172. Valve 152 permits flow of air through passage 164 only when the air pressure within shell 106 is greater than that in space 108, and then only as a result of centrifugal force acting upon weight 98. Spring 172 exactly supports piston 98 on a column of air when the longitudinal axis of piston 98 is in an exact perpendicular position.

The liquid vessel 102 (FIGURE 4) comprises an elongate cylindrical shell 174 fabricated from a rigid transparent material such as a polymerized resin, Lucite, or the like, the ends of which are closed by third and fourth end pieces176 and 178, respectively. End piece 176 is formed with a boss 176a that slidably and sealingly engages one interior end surface portion of shell 174. End piece 178 is likewise formed with a boss 178a that also engages the opposite interior end surface of shell 174. A second tubular nipple 180 having a threaded end 182 is threadedly connected to a tapped bore 184 formed in end piece 176. Bore 184 communicates with a passage 186 that extends through end piece 176 and boss 17611 to communicate with the interior of shell 174. A third nipple 188 or other suiltable fitting is provided that has a threaded portion 190 in which a check valve 191 is formed that includes a movable ball 192. Portion 190 threadedly engages a tapped recess 194 formed in end piece 176 and this recess communicates with a bore 198 that extends through end piece 176 and boss 176a to cornmunicate with the interior of shell 174. End piece 178 is provided with a tapped recess 200 that is threadedly engaged by a suitable threaded tubular fitting 202 with which a conduit 204 is removably connected that extends to port 89, as best seen in FIGURE 2.

A rigid elongate member 208 having a bore 210 of large transverse cross section extending longitudinally therethrough is disposed parallel to end pieces 110 and 176, as can best be seen in FIGURE 4. The upper end of bore 210 is removably closed by a plug 212 in which a circumferentially extending recess 214 is formed. A resilient sealing ring 216 is seated in recess 214 and effects a fluid seal with a section of the interior surface of bore 210. A tapped bore 218 extends transversely through the upper portion of member 208 and is threadedly engaged by a set screw 220 that bears against plug 212 to hold same in fixed position relative to member 208. The lower end of bore 210 is removably closed by a valve member 222 that is formed with a circumferential groove 224, a portion of which is engaged by the inner end of a set screw 226. Screw 226 is threadedly transversely positioned in a tapped bore 228 formed in the lower portion of member 208.

A passage 230 extends transversely through valve member 222, and this passage communicates with two diametrically opposed tapped bores 232 and 234 formed in the lower portion of member 208. Bore 232 is threadedly engaged by a threaded tubular fitting 233 that is connected to a conduit 236 which extends to port 80, as best seen in FIGURE 2. Bore 234 is threadedly engaged by the threaded end portion 188a of nipple 188. Two longitudinally spaced, circumferentially extending grooves 240 are formed in valve member 222 in which resilient sealing 242 are situated that seal with the interior surface of bore 210 (FIGURE 4). Valve member 222 includes an upwardly extending neck 244 through which a tapped bore 246 extends downwardly to intersect passage 230. A threaded orifice member 248 having a longitudinally extending fluid passage 250 formed therein is intermediately disposed in bore 246.

Bore 246 is engaged by an externally threaded tubular member 252, the upper end of which develops into an enlarged portion 254 that defines a valve seat 256 that tapers downwardly and outwardly, as also shown in FIG- URE 4. A bore 258 extends longitudinally through portion 254 and member 252, and at all times communicates with bore 250. A cylindrical support 260 is intermediately disposed in bore 210 and held in fixed position therein by a set screw 262 that extends through the side wall of member 208. A circumferentially extending groove 264 is formed in support 260, which groove receives a ring-shaped resilient sealing member 266 that is at all times in fluid sealing contact with a portion of the surface defining bore 210. Member 260 also has a longitudinally extending bore 268 formed therein that communicates with a counterbore 270 which in turn communicates with a central, upwardly extending recess 272. Bore 268 has a resilient fluid sealing ring 274 disposed therein as well as a tubular member 276.

A rigid rod 280 depends downwardly through bore 268 and counterbore 270 to terminate in an inverted cupshaped rigid valve member 282 having a resilient core 284 of rubber or a like material, situated within the confines thereof which is adapted to be brought into close contact with the valve seat 256 (FIGURE 4). The up per extremity of rod 280 bears against the lower face of a cup-shaped actuator 286 that is slidably mounted in bore 210. This actuator has a cylindrical side wall 288 in which a circumferentially extending groove 290 is formed that at all times communicates with a number of spaced bores 292 that are in communication with the interior of the actuator 286. When actuator 286 is in the position shown in FIGURE 4, groove 290 communicates with a passage 294 formed in elongate member 208 which extends to a tapped bore 296 also formed in this member that receives the threaded end of nipple 136. A transverse bore 298 is also formed in member 208 that communicates with a space 300 located within the confines of a bore 210 between the upper surface portion of valve member 222 and the lower face of support 260. Bore 298 slidably receives one end portion of second nipple 180. A circumferential groove 302 is formed in an end portion of nipple 180. Groove 302 receives a resilient fluid-sealing member 304 which bears against a surface portion of bore 298 to eflfect a fluid seal therewith.

The longitudinal axis 106a of first shell 106 (FIGURE 4) is parallel to the longitudinal axis 60a of piston rod 60. Axis 106:: extends through the center of gravity of weight 69. When crank arm 26 has rotated to a position on the circular path Z (FIGURE 6) where the longitudinal axis 106:! passes through a point D thereon, the weight 98 slides downwardly in first shell 106, lightly compressing the air therein, and causing the compressed air to discharge through valve 162 into the annulus-shaped space 108, when the crank arm and weight are in rotary motion and in a perpendicular position.

The volume of space 108 is greater than the volume of space in first shell 106 in which the air is situated that is compressed by centrifugal force acting upon the weight 98. Compressed air flows from space 108 through passages 128 and 130 to the tubular member 136 through which it flows to assages 292 that are in communication with the interior of actuator 286. Due to the compressed air pressure to which it is subjected, actuator 286 moves downwardly and brings valve member 282 and resilient core 284 into obstructing contact with'valve seat 256. Actuator 286 is slidably but loosely fitted in bore 210. Compressed. air above the actuator can bleed between the surface of bore 210 and the external surface of the actuator to escape through a vent 287 into the ambient atmosphere at a very slow rate.

At substantially the same time the weight 98 starts to slide in first shell 106 as above described, and weight 69 starts to slide outwardly along piston rod 60 in the direction of nut 62 as best shown in FIGURE 2. This movement of weight 69 toward nut 62 places pressure on the liquid in space 81 whereby the liquid tends to flow through conduit 236, fitting 233, passage 230 in valve body 222, orifice restriction 250 and bore 258. However, the ratio of weight 98 to weight 69 is so selected that when both are subjected to rotary motion, with both having substantially the same radius of rotation, the air in first shell 106 is compressed to the extent that valve member 9 core 234 is pressed against valve seat 256 with exactly sufficient force to counteract two times the pressure eilect developed within annulus 81 as a result or" the centrifugal force that is simultaneously acting in addition to the force of gravity to cause the weight 69 to move outwardly toward nut 62.

During the time the crank arm 26 moves between A-A on the 360 cycle shown in FIGURE 6, weights 69 and 48 in conjunction with the weight of the rest of the crank arm will, if weights 6% and 48 are correctly positioned, exactly balance all of the rod weight and onehalf of the weight of the fluid column (not shown) moved by rod R. Weights 69 and 48 tend to be drawn downwardly by gravity between A-A' as the fluid column is lifted, and accordingly balances one-half the weight of the fluid column in addition to all of the rod weight being raised by the upwardly moving rod R. Likewise, as the crank arm moves in the circular path Z from A to A, the weight of crank arm 26, together with the weight of weights 69 and 48, it correctly positioned thereon, will be over-balanced by an amount equal to one-half of the weight of the fluid column. The force of gravity on crank arm 26 and weights 69 and 48 between A-A acts thereon in a direction to oppose the force generated by the weight of the rod string which tends to move rod R downwardly. It will be apparent that there can be no fluid column weight during a downward stroke of the rods.

However, if crank arm 26 is overbalanced, that is, the weight 62 is'too far out on piston rod 60 toward nut 62, the crank arm 26 will accelerate from B to B on circular path Z. When point D is reached, weight 69 would tend to slide even further out on piston rod 66 toward nut 62, but due to the action of weight 98 and valve member 284, a resistance is set up whereby liquid is prevented from flowing freely from space 81 and such motion of weight 69 is retarded. The overbalanced position of weight 69 decelerates the motion of crank arm 26 as it moves from B to B, as best seen in FIGURE 6, thereby causing weight 69 to move toward nut 64 (inwardly) after it passes point D to point D".

When the longitudinal axis 166a of first shell 166 passes a point D on the circular path Z that is diametrically opposed to point D, weight 98 slides downwardly in first shell 166 until it contacts resilient stop 126; This downward movement of weight 98 in shell 166 creates a partial vacuum therein which is relieved as valve 154 opens to admit air therethrough into the confines of shell 1&6 until the air pressure within the shell is equalized with that of the ambient atmosphere.

When the overbalanced crank arm 26 rotates to the position where the longitudinal axis of first shell 166 passes through point D, the weight 69 tends to'slide inwardly on piston rod 64) toward nut 64 into a more balanced position. Such movement is accompanied by exertion of pressure on the hydraulic liquid in space 99 whereby the liquid tends to discharge therefrom through conduit 264 into reservoir 102. Orifice 366, best seen in FIGURE 4, restricts the rate of liquid discharge from conduit 264 to prevent a too rapid movement of weight 69 on piston rod 60.

Movement of weight 69 toward out 6- on piston rod 66 tends to create avacuum in space 81. However, this vacuum does not acutally occur, for liquid from reservoir 1&2 immediately flows through passage 138, check valve 191, passage 230 and conduit 236 into space 81.

When the crank arm 26 is underbalanced, that is, the weight 6? is too far inwardly on piston rod 6% toward nut 64, the following situation prevails. Weight 28 operates in the same manner as previously described, but the crank arm 26 decelerates between B and B and accelerates between B and B. Accordingly, the crankarm 26 is in the lower half of the cycle between C and C for a greater length of time than in the upper half between C and C. The crank arm .26 is in the lower half of the circular path Z sufliciently long for the compressed air above actuator 286 to bleed oif through vent 287 to the extent that the pressure on liquid in bore 258 will lift valve member 284 with less resistance to approximately the position shown in FIGURE 4. Such upward lifting of valve member 284 allows movement of weight 69 on piston rod 66 due to the force of gravity toward nut 62 into a more balanced position on crank arm 26.

From the above description of the preferred form of the invention it will be seen that any unbalance of the crank arm 26 brought about by variation in the physical condition of the well being pumped or otherwise, results in different time intervals for the crank arm 26 to rotate through the upper and lower halves of the circular path Z shown in FIGURE 6. This variation in time causes the mechanism M to react as above described to cause the weight 69 to move until this weight is in balance and the time intervals are again the same. When weight 69 is in balance, the prime mover 30 at all times works against a load that is equal to one-half the weight of the fluid column (not shown).

Reservoir 102 is provided at a convenient location with a conventional air vent V which permits air to flow into the interior of the reservoir .but prevents the flow of hydraulic liquid therefrom. Conduits 204 and 236 (FIG- URF. 2) are provided with normally open, manually operable shut-oil valves 204a and 236a, respectively. When the crank arm 26 is stationary, these valves may be closed to prevent escape of hydraulic liquid from spaces 81 and 90, and as a result thereof weight 69 is held in a desired fixed position on piston rod 60.

Although the operation of the present invention has been described in terms of a movable counterbalance weight 69 on crank arm 26, it will be obvious that the same operational principle will apply to the use of the present invention in connection with a movable counterbalance weight 189 on the walking beam 16, with the walking beam weight either supplementing the crank arm weight, or used alone without the crank arm weight. The walking beam weight will tend to move outwardly on the beam during the time that portion of the beam axis on which the weight is located is below. the horizontal center of the axis, and the weight will move inwardly during the time that portion of the axis on which the weight 69 is located above the previously mentioned horizontal center. Since the walking beam 16 follows the same periodic motion as the crank arm 26, the same principles will apply as above described in detail.

A-first alternate form of the invention is shown in FIGURE 7, in which the mechanism M is replaced by a mechanism M. This alternate form M allows for manual adjustment of the weight 69 on piston rod 60 by a single operator, and is accomplished when'the crank arm is in motion and tilted in a. direction by which theforce of gravity on weight 69 causes it to slide downwardly on piston rod 66 until a desired position is attained thereon. After weight 6% has moved to a desired position on piston rod 60, a manual control valve which will be described hereinafter is closed, and weight 69 is hydraulically locked in a fixed position on rod 60.

In the first alternate form of the invention (FIGURE 7), the conduit 236 (FIGURE 2 is extended to a T 320 having two oppositely extending legs 320a and 32612. A conduit 322 connects leg 320 to a one-way check Valve 324, which in turn is connectedto an orifice 326. A

three-way plug valve 328 is provided that has three ports 330, 332, and 336 formed in the body 329 thereof. A rotatable valve member 337 is mounted within the conlines of valve body 329. Valve member 337 has two passages 34%? and 342 formed therein and arranged in the shape of a T. A tube 344 extends from orifice 326 to a communicating position with port 330 through an L 331 aflixed thereto. A hydraulic liquid reservoir 346 in the form of a cylindrical shell is provided, the ends of which are closed by end pieces 350 and 352, as can best be seen in FIGURE 7.

End piece 350 has three independent bores 354, 354a and 355 extending therethrough. Bore 355 is connected to a conventional air vent 356 that permits entry of air from the ambient atmosphere into the confines of the reservoir, but prevents discharge of hydraulic liquid therethrough. The bore 354 is connected to a tubing fitting 358 that has a conduit 362 connected thereto. Conduit 362 extends to an L 366 which is connected to port 336. Bore 354a is connected to L 364 and port 332 by means of conduit 374.

A bore 368 extends through end piece 352 and is connected to a tubing L 370, which in turn is connected by tube 372 to a one-way check valve 374 from which a conduit 376 extends to join a Y fitting 37211 which joins conduit 204 and communicates with the annulu'sshaped space 90 shown in FIGURE 2. A conduit 380 is also provided that is connected to Y fitting 372a and conduit 204 upstream from check valve 374. Conduit 380 is connected to a one-Way check valve 382 which in turn is connected to a flow-restricting orifice 384 from which a conduit 386 extends to join L 364 and port 332 as shown in FIGURE 7.

. When it is desired to use the first alternate form of the invention to cause the weight 69 to intermittently move outwardly on piston rod 60 toward nut 62, the valve member 337 is manually rotated by means (not shown) to a position where passage 340 therein is aligned with ports 330 and passage 342 is aligned with port 336. As gravity causes weight 69 to slide intermittently downwardly o n piston rod 60, the space, 81 decreases in volume as liquid is forced therefrom under pressure due to movement of weight 69, while the volume of space 90 increases. As space 81 decreases in size a portion of the liquid thereln discharges through conduit 236. Fluid discharging from conduit 236 flows through T 320 and leg 320a thereof, conduit 322, one-way check valve 324, flow-restricting orifice 326, conduit 344, L 331, port 330, passages 340 and 342, port 336, L 366, conduit 362, fitting 358 and bore 354' into the confines of reservoir 346. As the aunulus-shaped space 90 increases in volume, a vacuum tends to form therein but is prevented by flow of liquid from reservoir 346 into space 90 through bore 368, fitting 37 0, tube 372 and one-way check valve 374, Y fitting 372a, conduit 376 and conduit 204. After weight 69 has intermittently moved a sufiicient distance on piston rod 60 to bring the mechanism into proper balance, plug valve 328 is then placed in a closed position with no ports in register.

When it is desired to cause weight 69 to move in the direction of nut 64 with the first alternate form of the invention,-weight 69 must slide intermittently inwardly on the rod. To permit gravitational force to adjust weight 69 toa desired position on rod 60, the valve member 337 is rotated to place passage 340 in communication with ports 332 and 336 respectively.

In moving on piston rod 60 toward nut 64, weight 69 decreases the volume of space 90 and increases the volume of space 81. Liquid from space 90 is consequently discharged therefrom and flows through conduit 204, one-way check valve 382, flow-restraining orifice 384, conduit 386, tubing L 364, port 332, passage 340 and port 336, L 366, conduit 362, fitting 358 and bore 354 into the confines of reservoir 346. An increase in the volume of space 81 reduces the pressure therein, but the space is constantly filled with liquid as it increases in volume by fluid flow from reservoir 346 through bore 354a, fitting 354b, conduit 374, one-way check valve 376, conduit 378, T connection 320 and leg 320 thereof and conduit 236 to space 81. After weight 69 has moved the desired distance on piston rod 60, it is hydraulically locked in this position by closing the previously opened valve 328.

The second alternate form of the invention, as can be seen in FIGURE 8, includes only the shell 70, piston rod 60, piston 66 and counterweight 69 previously described in detail, end pieces 400 and 400' which close the ends of 12 the shell. Two circumferentially extending grooves 402 and 404 are formed in end piece 400 in which resilient rings 406 and 408 respectively are positioned. Ring 408 seals against piston rod 60 and ring 406 bears against piston rod 60 and ring 406 bears against an interior end surface of shell 70.

A bore 410 extends through end piece 400, and an outer tapped portion 412 thereof is engaged by a tubing fitting 414. Fitting 414 is connected to a conduit 416 that extends to a T 418. One leg 420 of T 418 is connected to a tube 422 which extends to a grease fitting 424 of the well-known Alemite type. Another leg 426 of T 418 is connected to a conduit 428 that leads to a manually operable shut-off valve 430. The opposite end of shell '70 embodies the same assembly of elements as enumerated above. The elements on the opposite end of shell 70 are identified by the same numerals previously used for this purpose, but to which a prime has been added.

In using the second form of the invention the valves 430 and 430 are opened to the atmosphere and oil is discharged under pressure through fittings 424 and 424 to fill spaces 81 and 90, after which the vent valves are closed, and valves 430 and 430' are connected together by conduit 430". Thereafter, if it is desired to move the weight 69 on rod 60, the crank arm 26 is rotated to a position where it slopes downwardly in the desired direction. Valves 430 and 430' are then opened whereby weight 69 slides downwardly on rod 60 and expels oil from the top annulus to the lower annulus. In this manner no air is drawn into the annuluses 81 or 90. After weight 69 has slid downwardly on rod 60 to the desired position, valves 430 and 430 are closed. Due to its simplicity of structure the second alternate form of the invention is much less expensive to manufacture than the first alternate form thereof.

Should it be more convenient, the crank arm 26 can be rotated to a substantially horizontal position, one valve 430 or 430 then opened, and grease applied through the appropriate one of the fittings 424 or 424' to cause movement of weight 69 on rod 60 in the desired direction. After the weight has been moved the proper degree, valves 430 and 430' are closed, whereby the weight is held in a fixed position on rod 60 inasmuch as piston 66 is locked between two confined bodies of grease in spaces 81 and 90. It has been found from experience that a very heavy grade of grease may be used for this purpose.

Although my invention is fully capable of achieving the results and providing the advantages hereinbefore mentioned, it is to be understood that it is merely the presently preferred embodiment thereof, and that I do not mean to be limited to the details of construction above described other than as defined in the appended claims. I claim:

1. The method of automatically changing a weight balanced rotating crank arm that rotates in a substantially vertical plane from either an underbalanced or overbalanced to a perfectly balanced condition including the steps of: slidably mounting a counterbalance weight for longitudinal movement on said crank arm; providing first, second and third confined spaces on said crank arm; completely filling said first and second confined spaces with a hydraulic liquid; subjecting said liquid in said first space to the Weight of said counterweight minus the centrifugal force thereon during the period said crank arm is in the upper half of the cycle of rotation thereof; subjecting said liquid in said second space to the weight of said counterweight plus the centrifugal force thereon during the period said crank arm is in the lower half of the cycle of rotation thereof; discharging said liquid in said first space to said third space during said rotation of said crank arm through the upper half of said cycle; restricting said discharge of said liquid from said first to said third space to dampen the movement of said counterbalance weight relative to said crank arm; providing a movable member that can be moved to a first position where it obstructs the discharge of said liquid from said second space to said third space; generating a first force by the rotation of said crank arm through said lower half of said cycle thereof that is initially of such magnitude as to counteract twice the centrifugal force generated by said rotation of said counterbalance weight; applying said first force to said movable member during at least a portion of the period said crank arm is in said lower half of said cycle; moving said movable member to a second position during the period said crank arm is in the lower half of said cycle to permit said liquid in said second space to discharge into said third space; restricting the flow of said liquid from said second space to said third space to dampen the movement of said counterbalance weight relative to said crank arm; and allowing the force of gravity to move said counterbalance weight relative to said crank arm as said crank arm rotates until said weight assumes a position relative thereto at which said crank arm rotates through one-half the cycle of rotation thereof in the same time as required to rotate through the other one-half thereof.

2. A method as defined in claim 1 including the further step of providing said first force by means of a confined quantity of air under a pressure greater than that of the ambient atmosphere.

3. An apparatus for counterbalancing an elongate rigid member capable of arcuate movement about an axis transverse thereto, including: a piston; a rod that supports said piston at an intermediate position thereon; a cylindrical shell in which said piston is disposed to slidingly and sealingly engage the interior surface thereof, and from the ends of which shell portions of said rod project; first and second end pieces for closing the ends of said shell, which end pieces slidably and sealingly engage said rod; means for supporting said rod end portions outwardly from said member, with said rod being longitudinally disposed relative to said member; a counterbalance weight supported from said shell; first and second passage means in said first and second end pieces, respectively, through which a non-compressible fiowable material can be introduced to fill the interior of said shell on each side of said piston; first and second normally closed valve means that control flow of said material through said passages, with said fiowable material on each side of said piston in said shell holding said shell and weight at a fixed position relative to said member as said member moves, said first and second valve means being adapted to be opened to permit said fiowable material to discharge from one end thereof, with concurrent movement of said weight and shell relative to said member until said weight and shell are disposed at a true counterbalancing position thereon; and means for introducing said fiowable material into the one of said passage means through which said material does not fiow to maintain said cylinder full of said material when said valve means are closed, which material when said valve means are closed cooperates with said piston and shell to hold said weight in said true counterbalancing position to which it has been moved.

4. Apparatus for use in automatically counterbalancing a reciprocating machine, which machine includes a member that periodically swings about a pivot to tilt both ways from the horizontal and on which member a fixed counterbalance weight is mounted, said apparatus comprising:

(a) a piston rod supported in a fixed position relative to said member; (b) a piston rigidly mounted on said piston rod; (c) a counterbalance weight; (d) a hydraulic cylinder afiixed to said counterbalance weight and slidably engaging said piston; (e) end pieces disposed at both ends of said cylinder that cooperate with said piston and piston rod to define first and second confined spaces of variable lengths;

(f) a vessel supported from said member;

(g) first hydraulic liquid conducting means for connecting said first space to a position adjacent the interior of said vessel;

(h) second hydraulic liquid conducting means for connecting said second space to a position adjacent the interior of said vessel;

(i) hydraulic liquid in sufiicient quantity to completely fill said first and second spaces, at least a portion of said first and second means, and at least partially filling said vessel;

(j) hydraulic liquid flow restricting means for limiting the rate of flow of said hydraulic liquid from said first and second confined spaces to said vessel to dampen the movement of said counterbalance weight relative to said arm as said counterbalance weight tends to move by gravity as said member moves from one of said tilted positions towards the other of said tilted positions;

(k) and control means actuated by the swinging of said member for further restricting the flow of said hydraulic fluid through said first liquid conducting means and said flow restricting means for compensating for centrifugal force on said counterbalance weight as said member periodically swings to permit said counterbalance weight and said cylinder to slide by gravity alone on said piston rod to a position where said counterbalance weight counterbalances said member.

5. The device of claim 4 wherein said piston rod is affixed at its ends to said periodically swinging member, with said piston being disposed intermediate said ends of said piston rod, and said piston rod extends through openings through each of said cylinder end pieces.

;6. 'lhe device of claim 4 wherein said periodically swinging member is a rotating crank arm of said reciproeating machine.

7. The device of claim 4 wherein said periodically swinging member is a walking beam of said reciprocating machine.

8. The device of claim 4 which includes shut-off means on said first and second means for stopping the flow of said liquid from said first and second spaces when said machine ceases to operate, whereby said counterbalance weight will be locked in a fixed position when said machine is not operating. I

9. An apparatus as defined in claim 4 wherein said counterbalance weight position control means includes: a secondary cylinder closed at both ends afiiXed to said counterbalance weight; a piston freely and slidably mounted in said secondary cylinder that compresses air in said secondary cylinder as said crank arm rotates; first valve means that admits air into said secondary cylinder when the air pressure therein falls below the pressure of the hath Zll'lluififit atmosphere; second valve means which is spring loaded and in communication with the interior of said secondary cylinder, which valve means permit discharge of air therefrom when said air is compressed to a predetermined pressure; third valve means which is air-actuated and in communication with said second liquid conducting means and said vessel, which third valve means obstructs liquid flow from said second means to said vessel when subjected to air at said predetermined pressure; and air conducting passage means connecting said second and third valve means, with the magnitude of the weight of said piston and the loading on said second valve means being so chosen that said air discharged to said third valve means is at said predetermined pressure, with said predetermined pressure being so related to the pressure placed on said liquid in said confined space by said centrifugal force thereon that said third valve sets up a resistance to passage of liquid that is equal to two times the pressure developed by the centrifugal force acting.

' on the counterbalance weight during the portion of said cycle of rotation of said crank arm in which said liquid in said confined space is subjected to a force that is the sum of the weight of said counterbalance weight plus ;twice the centrifugal force exerted thereon due to the rotation of same.

10. An apparatus as defined in claim 4' wherein vent means are provided on said third valve means to continuously bleed oif said air at said predetermined pressure to the ambient atmosphere at a very slow rate.

11. The method of automatically changing a weight balanced rotating crank arm that rotates in a substantially vertical plane from either an underbalanced or overbalanced to a perfectly balanced condition which includes the steps of:

(a) slidably supporting a counterbalance weight for longitudinal movement on said crank arm;

(b) dampening the sliding movement of said counterbalance weight in both directions on said crank arm as said crank arm rotates;

(c) determining whether said crank arm takes a great er or lesser length of time to rotate through the lower half of each revolution than through the upper half thereof;

(d) imposing a force on said counterbalance weight when it is in the lower half of said revolution and said crank arm is rotating in such a manner that saidcrank arm takes less time to rotate through the lower half of a revolution thereof than through i the upper half of said revolution;

(e) generating said force by the rotation of said crank arm; and

(f) applying said force to said counterbalance weight in a direction to nullify twice the centrifugal force on said counterbalance weight when said counterbalance weight is in the lower half of each of said revolutions to permit said counterbalance weight to slide by the force of gravity to a position where 'said crank arm is perfectly balanced. I

References Cited by the Examiner t UNiTED STATES PATENTS 1,706,407 3/29 Miller ct al. 74590 1,890,428 12/32 Ferris et al.

2,007,493 7/35 Bier 74-41 X 2,432,735 12/47 Downing 741l0 2,915,919 12/59 Mitchell et al. 74-590 BROUGHTON G. DURHAM, Primary Examiner. 25 SAMUEL SPINTMAN, Examiner. 

1. THE METHOD OF AUTOMATICALLY CHANGING A WEIGHT BALANCED ROTATING CRANK ARM THAT ROTATES IN A SUBSTANTIALLY VERTICAL PLANE FROM EITHER AN UNDERBALANCED OR OVERBALANCED TO A PERFECTLY BALANCED CONDITION INCLUDING THE STEPS OF: SLIDABLY MOUNTING A COUNTERBALANCE WEIGHT FOR LONGITUDINAL MOVEMENT ON SAID CRANK ARM; PROVIDING FIRST, SECOND AND THIRD CONFINED SPACES ON SAID CRANK ARM; COMPLETELY FILLING SAID FIRST AND SECOND CONFINED SPACES WITH A HYDRAULIC LIQUID; SUBJECTING SAID LIQUID IN SAID FIRST SPACE TO THE WEIGHT OF SAID COUNTERWEIGHT MINUS THE CENTRIFUGAL FORCE THEREON DURING THE PERIOD SAID CRANK ARM IS IN THE UPPER HALF OF THE CYCLE OF ROTATION THEREOF; SUBJECTING SAID LIQUID IN SAID SECOND SPACE TO THE WEIGHT OF SAID COUNTERWEIGHT PLUS THE CENTRIFUGAL FORCE THEREON DURING THE PERIOD SAID CRANK ARM IS IN THE LOWER HALF OF THE CYCLE OF ROTATION THEREOF; DISCHARGING SAID LIQUID IN SAID FIRST SPACE TO SAID THIRD SPACE DURING SAID ROTATION OF SAID CRANK ARM THROUGH THE UPPER HALF OF SAID CYCLE, RESTRICTING SAID DISCHARGE OF SAID LIQUID FROM SAID FIRST TO SAID THIRD SPACE TO DAMPEN THE MOVEMENT OF SAID COUNTERBALANCE WEIGHT RELATIVE TO SAID CRANK ARM; PROVIDING A MOVABLE MEMBER THAT CAN BE MOVED TO A FIRST POSITION WHERE IT OBSTRUCTS THE DISCHARGE OF SAID LIQUID FROM SAID SECOND SPACE TO SAID THIRD SPACE; GENERATING A FIRST FORCE BY THE ROTATION OF SAID CRANK ARM THROUGH SAID LOWER HALF OF SAID CYCLE THEREOF THAT IS INITIALLY OF SUCH MAGNITUDE AS TO COUNTERACT TWICE THE CEN- 